Guidewire with deflectable tip having improved torque characteristics

ABSTRACT

A bi-directional steerable guidewire having a deflectable distal tip which comprises a longitudinal hypotube and an interlocking spring coil attached to the distal end of the hypotube and also includes a longitudinally movable deflection member which is attached to the distal end of the spring coil and a tip retaining member which extends from the distal end of the hypotube to the distal end of the spring coil for providing very precise deflection of the distal tip.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This patent application is a continuation-in-part of U.S. patentapplication Ser. No. 10/224,168, filed on Aug. 20, 2002, now U.S. Pat.No. 7,128,718 entitled, “Guidewire With Deflectable Tip,” which is anonprovisional patent application of U.S. patent application Ser. No.60/366,739, filed on Mar. 22, 2002, entitled, “Deflection Wire Concept.”

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a steerable guidewire having improvedtorque characteristics, and more particularly to a bi-directionalsteerable guidewire having a tip which may be very precisely “steered,”and deflected. The guidewire is particularly suitable for use inconjunction with the insertion of a catheter into a vessel of the body,or alternatively, the guidewire may be used by itself to openobstructions within a vessel or to carry a therapeutic device forremoving obstructions within a vessel.

2. Description of the Prior Art

For many years guidewires have included a core wire with the distal endbeing tapered and with a coil spring mounted on the tapered distal end.These guidewires have been used to facilitate the insertion of acatheter into a vessel of the body. Generally, the guidewire is insertedinto a vessel, a catheter is inserted over the guidewire and thecatheter is then moved through the vessel until the distal end of thecatheter is positioned at a desired location. The guidewire is thenretracted from the catheter and the catheter is left in the vessel.Alternatively, the guidewire may be first inserted into the catheterwith the distal portion of the guidewire extending beyond the distal endof the catheter. This assembly is then inserted into a vessel with thedistal tip of the guidewire being used to facilitate movement of theguidewire and catheter through the vessel. Again, when the distal tip ofthe catheter has been placed in a desired location, the guidewire may beretracted thereby leaving the catheter in place within the vessel.

Another common application for guidewires is that of using the distaltip of the guidewire for removing an obstruction within a vessel. Oftentimes this procedure is accomplished by inserting the guidewire within avessel, moving the distal tip of the guidewire into contact with theobstruction and then very gently tapping the distal tip of the guidewireagainst the obstruction until the guidewire passes through theobstruction. Alternatively, various types of devices may be placed onthe distal end of a guidewire for actively opening an obstruction withinthe vessel. Examples of such devices which may be placed on the end ofthe guidewires in order to open an obstruction are disclosed in thefollowing Robert C. Stevens U.S. Pat. Nos. 5,116,350; 5,078,722;4,936,845; 4,923,462; and, 4,854,325.

While most guidewires used today do not include a mechanism fordeflecting or steering the tip of the guidewire, it is very desirable toprovide tip steering in order to facilitate movement of the guidewirethrough the tortuous vessels of the body. There are many patentsdirected toward different mechanisms for deflecting the distal tip of aguidewire in order to steer the guidewire. Examples of such guidewiresare disclosed in the following patents: U.S. Pat. No. 4,815,478 toMaurice Buchbinder, et al., U.S. Pat. No. 4,813,434 to MauriceBuchbinder, et al., U.S. Pat. No. 5,037,391 to Julius G. Hammerslag, etal., U.S. Pat. No. 5,203,772 to Gary R. Hammerslag, et al., U.S. Pat.No. 6,146,338 to Kenneth C. Gardeski, et al., U.S. Pat. No. 6,126,649 toRobert A. VanTassel, et al., U.S. Pat. No. 6,059,739 to James C. Baumannand U.S. Pat. No. 5,372,587 to Julius G. Hammerslag, et al. U.S. Pat.No. 4,940,062 to Hilary J. Hampton, et al., discloses a balloon catheterhaving a steerable tip section. All of the above-identified patents areincorporated herein by reference.

While each of the latter group of patents disclose guidewires havingsome degree of steerability, there is a need to have a guidewire withvery precise steering in a guidewire of a very small diameter which issuitable for the purposes described above. More particularly, there isan important need for a very small diameter guidewire having improvedtorque characteristics which includes a distal tip which may bedeflected very precisely in either of two directions to enhancesteerability.

SUMMARY OF THE INVENTION

In accordance with one aspect of the present invention, there isprovided a very small diameter steerable guidewire having a deflectabletip which includes an elongated flexible tubing, a flexible helical coilattached to the distal portion of the flexible tubing, an elongateddeflection member which is slidably disposed within the tubing andwithin the helical coil. The flexible helical coil is formed from anelongated member having a rectangular, or square cross section, andhaving continuous undulations wherein the undulations of adjacent turnsinterlock with each other, i.e., peak undulation of one turninterlocking with valley undulation of adjacent turn, to thereby enhancethe rotational rigidity, referred to as torque characteristic, of thecoil. The proximal portion of the deflection member is of a cylindricalconfiguration and the distal portion is tapered to form a deflectionribbon. Alternatively, the deflection member may take the form of aproximal cylindrical wire which is attached at its distal end to adeflection ribbon. In addition, a retaining ribbon is attached to thedistal end of the flexible tubing and is oriented to extend in a planewhich is generally parallel to the plane of the ribbon portion of thedeflection member. An attachment member which may take the form of arounded bead, preferably formed from epoxy, is bonded to the distal endof the helical coil, the distal end of the deflection ribbon and thedistal end of the retaining ribbon so that longitudinal movement of thedeflection member causes the distal end of the helical coil to bedeflected. With the enhanced rotational rigidity of the coil portion orthe guidewire, the entire guidewire has enhanced rotational rigidity.

In accordance with another aspect of the present invention, thecontinuous undulations take the form of a sinusoidal wave, oralternatively a square sinusoidal wave, having positive and negativepeaks and in which the positive peaks of adjacent turns of coils engagenegative peaks, or valleys, of adjacent turns.

In accordance with another aspect of the present invention, theretaining ribbon and the deflection ribbon are preferably pre-shapedinto a curved configuration to thereby cause the flexible helical coilto be biased into a normally curved shape.

In accordance with a further aspect of the present invention, the distalportion of the deflection ribbon engages the attachment member, orrounded bead, at a location offset from the center of the attachmentmember, and the distal portion of the retaining ribbon engages theattachment member at a location offset from the center of the attachmentmember. Preferably, the retaining ribbon engages the attachment memberat a location offset from the center portion of the attachment member inthe opposite direction from the offset location of the deflectionribbon.

In accordance with still another aspect of the present invention, thedeflection ribbon and the retaining ribbon are connected to each otherwithin the attachment member. Preferably these two elements are formedas a single unitary element. In a preferred embodiment of the inventionthe cylindrical deflection member is flattened to form the deflectionribbon and is further flattened at its distal end to form the retainingribbon. The retaining ribbon is bent 180 degrees with respect to thedeflection ribbon to form a generally U-shaped bend to thereby establisha predetermined spacing between the ribbons and to also cause theseribbons to remain parallel to each other.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an enlarged elevational view of a balloon on a guidewirehaving a deflectable tip and control handle in accordance with the oneaspect of the present invention;

FIGS. 2 and 2A are enlarged elevational sectional views showing thedistal end of the balloon on a guidewire in its normal pre-shapedposition;

FIG. 3 is an enlarged sectional view showing the distal end of thesteerable guidewire of FIG. 2 rotated 180 degrees; and,

FIGS. 4 and 5 are sectional views showing the steerable guidewiredeflected from its normal position to opposite extremes of deflection.

DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 generally illustrates a steerable guidewire system 10 whichembodies the present invention and comprises a steerable guidewire 12coupled to a control handle 14. More particularly, the steerableguidewire comprises an elongated hypotube 16, a helical coil 18 attachedto and extending from the distal end of the hypotube 16. The helicalcoil 18 is of a rectangular or square cross-sectional configuration andis preferably formed from platinum tungsten with the proximal turnsbeing wound such that adjacent turns of the proximal portion are incontact, or loosely interlocked with each other.

While the preferred embodiment of the present invention includes thehelical coil 18, this element may take the form of any flexiblerectangular or square cross-sectional member, such as for example a thinsquare metallic tube with or without portions of the tube removed, forexample laser cutting, so as to form a very flexible cylindrical orsquare member. An elongated deflection member 20 extends from theproximal end of the control handle through the hypotube 16 and throughthe helical coil 18, and is connected into an attachment member, orrounded bead 22, which is disposed at the distal tip of the helical coil18. In addition, a retaining ribbon 24 is connected to the distal end ofthe hypotube 16 and is also connected to the rounded bead 22.

The control handle 14 generally comprises a slidable control knob 26which may be moved longitudinally with respect to the control handle.The control handle 14 is coupled to the deflection member 20. As will bediscussed in more detail, the longitudinal movement of the slidablecontrol knob 26 causes deflection of the distal tip of the guidewire ineither an upward or downward direction.

FIGS. 2, 2A and 3 illustrate in more detail the distal portion of thesteerable guidewire 12. As may be appreciated, FIG. 3 is a view of theguidewire 12 shown in FIG. 2 with the guidewire being rotated 90 degreesabout its longitudinal axis. More particularly, the proximal end of thehelical coil 18 is bonded, preferably by use of an epoxy, to the outersurface near the distal end of the hypotube 16. The elongated deflectionmember 20 takes the form of a small diameter cylindrical deflectionmember 20 having an intermediate portion which is flattened to form athin deflection ribbon 34 having a thickness of approximately 0.002inches. The distal end of the cylindrical deflection member 20 isfurther flattened to a thickness of approximately 0.0015 inches and isbent back 180 degrees to form a U-shaped bend 26 a between thedeflection ribbon 34 and the retaining ribbon 24. The proximal end ofthe retaining ribbon 24 is bonded, preferably by use of epoxy, to theouter surface of the distal end of the hypotube 16. The retaining ribbon24 is aligned in a plane parallel to the plane of the deflection ribbon34 and the U-shaped portion between the ribbons is encapsulated by theattachment member which preferably takes the form of a rounded epoxybead 22 bonded to the distal tip of the helical coil 18.

As may be appreciated, with this unitary construction of the ribbonmembers, these members remain aligned so that both lie in planesparallel to each other. In addition, the U-shaped bend portion whenencapsulated into the rounded bead 22 causes the retaining ribbon anddeflection ribbon to be properly spaced with respect to each other.

As illustrated in FIG. 2, the retaining ribbon 24 is preferably attachedto the rounded bead 22 at a position offset from the center of the beadin the same direction that the retaining ribbon 24 is offset from thelongitudinal axis of the steerable guidewire 12. In addition, thedeflection ribbon 34 is attached to the bead at a position offset fromthe center of the bead in an opposite direction from the offset of theretaining ribbon 24.

Also, as may be seen in FIG. 2, the deflection ribbon 34 and theretaining ribbon 24 are pre-shaped into an arcuate, or curved,configuration to thereby maintain the helical coil 18 in a normallycurved configuration. The ribbons 24, 34 are pre-shaped such that thedistal tip of the guidewire curves away from the longitudinal axis ofthe guidewire in a direction toward that side of the guidewirecontaining the retaining ribbon 24.

The helical coil 18 is formed as an elongated member having arectangular, or square, cross-sectional configuration and wound in ahelical configuration. In addition as illustrated in FIG. 2A, theelongated member is formed with re-occurring steps, or step undulations,which when wound into a helical configuration so that adjacent turns toloosely interlock thereby preventing movement between adjacent turns.Such interlocking turns enhance the rotational rigidity or“torqueability” of the coil such that when the proximal end of the coilis rotated 180 degrees, the distal end of the coil will rotateapproximately 180 degrees. Accordingly, the distal end of the coil morenearly tracks, rotationally, the proximal end of the coil therebysignificantly improving the “tortional” characteristics of the coil. Byimproving the “tortional” characteristics of the coil, the overall“tortional” characteristics of the guidewire are significantly improved.

As opposed to winding an elongated member to form the helical coil 18, apreferred method of forming the helical coil is by laser cutting thecoil from a single thin-walled tube of an alloy in the undulationslocking, stepped configuration as illustrated in FIG. 2A. Such lasercutting provides a coil with precise mating surfaces to assure properinterlocking between adjacent turns of the helical coil.

In operation, as previously described, the distal tip of the steerableguidewire 12 is normally biased into a downwardly curved position asillustrated in FIG. 2 because of the curve of the pre-shaped deflectionribbon 34 and the retaining ribbon 24. When the slidable control knob 26is moved distally as shown in FIG. 5, the deflection member 20 will bemoved distally thereby causing the deflection ribbon 34 to move in adistal direction. As the deflection ribbon is moved distally, a pushingforce is applied to the top portion of the rounded bead 22. Theretaining ribbon 24 is attached to the lower portion of the bead 22 tothereby maintain the bead at a fixed distance from the distal end of thehypotube 16. As the deflection ribbon 34 is moved to the right, the tipof the guidewire is caused to deflect downwardly to a maximum deflectedposition.

Since the deflection ribbon 34 and the retaining ribbon 24 arepre-shaped prior to any activation of the steerable guidewire, theamount of force required to deflect the guidewire in this direction isvery small thereby preventing buckling of the deflection ribbon 34 asthe deflection ribbon is pushed distally. As the deflection ribbon 34 ismoved distally, the upper turns of the helical coil become slightlystretched and the lower turns of the coil become slightly compressed.The deflection member 20 has a diameter of about 0.0065 inches and thedeflection ribbon has a thickness of about 0.002 inches to therebyprovide sufficient stiffness to prevent the buckling of these elementswhen the deflection member 20 is pushed distally. This construction alsoprovides sufficient stiffness to transmit the necessary force from theproximal end to the distal end of the guidewire.

When the slidable control knob 26 is moved in a proximal direction asshown in FIG. 4, the deflection member 20 will be pulled to the left tothereby cause the deflection ribbon 34 to pull on the top portion of thebead 22. Since again the retaining ribbon 24 causes the lower portion ofthe bead to remain at a fixed distance from the distal end of thehypotube 16, the tip of the guidewire 12 is caused to bend in an upwarddirection to a maximum deflection as shown in FIG. 4. Since thedeflection ribbon 34 is in tension when the deflection member 20 ispulled, there is no concern for buckling of the deflection ribbon 34. Asthe deflection ribbon 34 is moved proximally, the upper coil turnsbecome slightly compressed and the lower coil turns become somewhatstretched.

As previously discussed, when the proximal end of the guidewire 12 isrotated by a physician to “steer” the distal end of the guidewire, withthe interlocking turns of adjacent coils of the helical coil 18, thedistal tip will rotate on a one-to-one basis with respect to theproximal end of the hypotube 16. In other words, there is no “play” or“lag” between rotation of the proximal end and the distal end of theguidewire.

In a preferred embodiment of the present invention, the elongateddeflection member 20, retaining ribbon 24 and deflection ribbon 34 areconstructed of nitinol, but these elements may be formed from otherflexible materials including polymers. The helical coil 18 preferablyformed by laser cutting as previously discussed, is constructed from analloy comprised of about 92 percent platinum and 8 percent tungsten, butthis element may also be constructed from numerous other materials. Itis desirable that the coil exhibit the characteristic of beingradiopaque to X-rays to assist in the positioning of the distal tip ofthe steerable guidewire 12. The deflection member 20 is formed from asingle cylindrical nitinol wire of about 0.0065 inches in diameterhaving an intermediate portion which is flattened to form the deflectionribbon 34 with a thickness of about 0.002 inches, and a distal portionwhich is flattened to form the retaining ribbon 24 with a thickness ofabout 0.0015 inches. The retaining ribbon 24 is bent back 180 degrees toform a generally U-shaped bend, which is subsequently encapsulatedwithin the rounded bead 22. The rounded bead 22 is preferably formedwith epoxy, but may be formed with soldering or by welding.

It has been found that the addition of graphite between the deflectionmember 20 and deflection ribbon 34, and the inner lumen of the hypotube16 provides lubrication. Other lubricants, such as Teflon or MDX may beused for this purpose. The helical coil 18 is preferably coated with anelastomeric polymer 41 on its distal end to act as a sealant preventingthe entry of blood and contrast media into the guidewire and afluorinated polymer 39, such as Teflon, on its proximal end forlubrication purposes.

It may be seen that the guidewire as disclosed may be very easily andvery precisely rotated and then deflected in either of two directionsfor very precise steering of the guidewire through the vessels of thebody. As may be apparent, the disclosed guidewire may be used forplacement of a catheter within the vasculature of the human body, it maybe used by itself to cross an obstruction within the vessels or it maybe used to carry a therapeutic device mounted on the distal end of theguidewire for purposes of removing obstructions which may exist within avessel of the body.

The preceding specific embodiment is illustrated of the practice of thisinvention. It is to be understood, however, that other variations mayalso be employed without departing from the spirit and scope of theinvention as hereinafter claimed.

1. A bi-directional steerable guidewire having a deflectable tip whichcomprises: an elongated flexible tubing having proximal and distalportions; a flexible helical coil having multiple turns and havingproximal and distal ends, said helical coil having a rectangularcross-sectional configuration and having continuous undulations whereinthe undulations of adjacent turns interlock with each other in order toenhance the rotational rigidity of the coil, the proximal end of saidhelical coil is attached to the distal portion of the flexible tubing;said undulations are lateral to the length of the elongated flexibletubing; said undulations taking the form of a sinusoidal wave havingpositive and negative peaks and in which the positive peaks of adjacentturns of coils engage negative peaks of adjacent turns; an elongateddeflection member having proximal and distal portions and being slidablydisposed within said tubing and within said helical coil, the distalportion of said deflection member being flattened to form a deflectionribbon which extends in a plane; a retaining ribbon for the steerableguidewire having proximal and distal ends, the proximal end of theretaining ribbon is attached to the distal portion of the flexibletubing and the retaining ribbon is oriented to extend in a plane whichis generally parallel to the plane of the deflection ribbon; and, anattachment member for the steerable guidewire engaging the distal end ofthe helical coil, the distal portion of the deflection member and thedistal end of the retaining ribbon so that longitudinal movement of thedeflection member in a distal direction causes the distal end of thehelical coil to be deflected in one direction and longitudinal movementof the deflection member in a proximal direction causes the distal endof the helical coil to deflect in another opposite direction.
 2. Abi-directional steerable guidewire as defined in claim 1, wherein thecontinuous undulations take the form of a square sinusoidal wave.
 3. Abidirectional steerable guidewire as defined in claim 1, wherein thehelical coil has a square cross-sectional configuration.
 4. Abi-directional steerable guidewire as defined in claim 1, wherein theretaining ribbon and the deflection ribbon are normally biased in anarcuate configuration to thereby cause the distal end of the helicalcoil to be normally biased in a curved shape.
 5. A bi-direotionalsteerable guidewire as defined in claim 1, wherein the proximal portionof said deflection member is of a circular cross section which extendsfrom the proximal portion of the flexible tubing to approximately thedistal portion of the tubing.
 6. A bi-directional steerable guidewire asdefined in claim 5, wherein the proximal end of said retaining ribbonextends from the distal portion of the flexible tubing to approximatelythe distal end of the flexible helical coil.
 7. A bi-directionalsteerable guidewire as defined in claim 1, wherein the attachment membertakes the form of a rounded bead.
 8. A bi-directional steerableguldewire as defined in claim 7, wherein the rounded bead is formed withan epoxy material.
 9. A bi-direotional steerable guidewire as defined inclaim 1, wherein the attachment member takes the form of a rounded beadwhich contacts the distal end of the helical coil to define a circularsurface at the distal end of the coil arid the deflection ribbon engagesthe rounded bead at a location offset from the center of the circularsurface of the rounded bead.
 10. A bi-directional steerable guidewire asdefined in claim 9, wherein the distal end of the retaining ribbonengages the rounded bead at a location offset from the center of thecircular surface of the rounded bead.
 11. A bi-directional steerableguidewire as defined in claim 10, wherein the distal end of theretaining ribbon engages the rounded bead at a location offset from thecenter of the circular surface in an opposite direction from the offsetlocation of the deflection ribbon.
 12. A bi-directional steerableguidewire as defined in claim 11, wherein the deflection member and theretaining ribbon are joined to each other within the rounded bead.
 13. Abi-directional steerable guidewire as defined in claim 12, wherein thedeflection ribbon and the retaining ribbon are formed as a singleunitary element.
 14. A N-directional steerable guidewire as defined inclaim 13, wherein the deflection ribbon and the retaining ribbon arejoined to form a generally U-shaped configuration to thereby provide apredetermined spacing between the deflection ribbon and the retainingribbon and to maintain the deflection ribbon and the retaining ribbon inplanes which are parallel to each other.
 15. A bi-directional steerableguidewire as defined in claim 14, wherein the deflection ribbon isformed by flattening an intermediate portion of the deflection memberand the retaining ribbon is formed by flattening a distal portion of thedeflection member.
 16. A bi-directional steerable guidewire as definedin claim 15, wherein the retaining ribbon is of a thickness which isless than the thickness of the deflection ribbon.
 17. A bi-directionalsteerable guidewire as defined in claim 16, wherein the deflectionribbon is of a thickness of 0.002 inches and the retaining ribbon is ofa thickness of 0.0015 inches.
 18. A steerable guidewire having adeflectable tip which comprises: an elongated flexible member formingthe steerable guidewire and having proximal and distal portions; aflexible helical coil having multiple turns and having proximal anddistal ends, said helical coil having a rectangular cross-sectionalconfiguration and having continuous undulations wherein the undulationsof adjacent turns interlock with each other in order to enhance therotational rigidity of the coil, said undulations are lateral to thelength of the elongated flexible member; said undulations taking theform of a sinusoidal wave having positive and negative peaks and inwhich the positive peaks of adjacent turns of coils engage negativepeaks of adjacent turns; a proximal end of said helical coil is attachedto the distal portion of the elongated flexible member; and, a roundedbead engaging the distal end of the helical coil of the steerableguidewire.
 19. A steerable guidewire as defined in claim 18, wherein thecontinuous undulations take the form of a square sinusoidal wave.
 20. Asteerable guidewire as defined in claim 18, wherein the helical coil hasa square cross-sectional configuration.
 21. A steerable guidewire havinga deflectabie tip which comprises: an elongated flexible tubing havingproximal and distal portions; a flexible helical coil having multipleturns and having proximal and distal ends, said helical coil having arectangular cross-sectional configuration and having continuousundulations wherein the undulations of adjacent turns interlock witheach other in order to enhance the rotational rigidity of the coil, theproximal end of said helical coil is attached to the distal portion ofthe flexible tubing; said undulations are lateral to the length of theelongated flexible tubing; said undulations taking the form of asinusoidal wave having positive and negative peaks and in which thepositive peaks of adjacent turns of coils engage negative peaks ofadjacent turns; an elongated deflection member comprised of proximal anddistal portions and being slidably disposed within said tubing andwithin said helical coil, the proximal portion of the deflection memberbeing of a cylindrical cross section and the distal portion of saiddeflection member takes the form a deflection ribbon which extends in aplane; a retaining ribbon for the steerable guidewire having proximaland distal ends, the proximal end of the retaining ribbon is attached tothe distal portion of the flexible tubing and the retaining ribbon isoriented to extend in a plane whim is generally parallel to the plane ofthe deflection ribbon; and, an attachment member for the steerableguidewire engaging the distal end of the helical coil, the distalportion of the deflection member and the distal end of the retainingribbon so that longitudinal movement of the deflection member in adistal direction causes the distal end of the helical coil to bedeflected in one direction and longitudinal movement of the deflectionmember in a proximal direction causes the distal end of the helical coilto deflect in another opposite direction.
 22. A steerable guidewire asdefined in claim 21, wherein the continuous undulations take the form ofa square sinusoidal wave.
 23. A steerable guidewire as defined in claim21, wherein the helical coil has a square cross-sectional configuration.24. A steerable guidewire as defined in claim 21, wherein the retainingribbon and the deflection ribbon are normally biased in an arcuateconfiguration to thereby cause the distal end of the helical coil to benormally biased in a curved shape.
 25. A steerable guidewire as definedin claim 21, wherein the distal portion of the deflection member and thedeflection ribbon are formed from a wire of a circular cross section andin which the distal portion is flattened to form the deflection ribbon.26. A steerable guidewire as defined in claim 25, wherein the attachmentmember takes the form of a rounded bead which contacts the distal end ofthe helical coil to define a circular surface at the distal end of thecoil and the deflection ribbon engages the rounded bead at a locationoffset from the center of the circular surface of the rounded bead. 27.A steerable guidewire as defined in claim 26, wherein the distal end ofthe retaining ribbon engages the rounded bead at a location offset fromthe center of the circular surface of the rounded bead.
 28. A steerableguldewire as defined in claim 27, wherein the distal end of theretaining ribbon engages the rounded bead at a location offset from thecenter of the circular surface in an opposite direction from the offsetlocation of the deflection ribbon.
 29. A steerable guidewire as definedin claim 28, wherein the deflection member and the retaining ribbon arejoined to each other within the rounded bead.
 30. A steerable guidewireas defined in claim 29, wherein the deflection ribbon and the retainingribbon are joined to form a generally U-shaped configuration to therebyprovide a predetermined spacing between the deflection ribbon and theretaining ribbon and to maintain the deflection ribbon and the retainingribbon in planes which are parallel to each other.
 31. A steerableguidewire as defined in claim 30, wherein the deflection ribbon isformed by flattening an intermediate portion of the deflection memberand the retaining ribbon is formed by flattening a distal portion of thedeflection member.
 32. A steerable guidewire as defined in claim 31,wherein the retaining ribbon is of a thickness which is less than thethickness of the deflection ribbon.
 33. A steerable guidewire as definedin claim 23, wherein the proximal portion of the elongated flexibletubing is coupled to a control handle and the elongated deflectionmember is mounted with the control handle for longitudinal movement. 34.A steerable guidewire as defined in claim 33, wherein said controlhandle includes a movable knob which is coupled to the elongateddeflection member for longitudinal positioning of the deflection member.